Trent Richardson and NFL Stars with the Biggest Injury Question Marks

Cleveland Browns running back Trent Richardson added his name Thursday to a long list of NFL stars on the comeback trail from injuries. The third overall pick underwent arthroscopic surgery to clean up his previously repaired knee.

Below, we break down Richardson's injury and the other NFL stars with injury question marks as the regular season gets closer.

Trent Richardson, RB, Cleveland Browns

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On Thursday, Richardson underwent "minor" surgery with Dr. James Andrews to remove a "hang nail particle" in his knee, according to Chris Mortensen of ESPN. While not connected to the torn meniscus he suffered in the BCS Championship Game last January, the surgery came on the same knee. There was irritation and swelling, which necessitated the surgery.

Dr. Michael Kaplan of ESPN said in the video included in Mortensen's piece that Richardson could need at least three-to-four weeks to fully recover, and the knee may still be a problem down the road this season.

Overall, the surgery was the right move by Richardson and the Browns training staff—but this is also his second knee scope in six months. That's concerning for a rookie running back who has yet to play in an NFL game and was drafted third overall.

Ryan Mathews, RB, San Diego Chargers

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There was a sense of building optimism in Mathews this offseason, especially after Mike Tolbert left San Diego for Carolina in free agency. This was supposed to be a backfield Mathews commanded.

Thursday night, much of that optimism went out the door. The injury bug bit again.

Mathews suffered a broken clavicle early against the Green Bay Packers, according to Michael Gelhken of the San Diego Union-Tribune. He's expected to miss four-to-six weeks, and it's entirely possible that Mathews will miss the start of the regular season.

One freak injury like Thursday night isn't reason for concern, but this is just the latest in a long line of ailments in Mathews' short NFL career.

The talent and opportunity are all there for Mathews. Staying on the field for an extended period of time is the next challenge.

Michael Vick, QB, Philadelphia Eagles

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The Eagles survived a brief scare from Vick Thursday night.

Vick banged his throwing thumb on an offensive lineman's helmet during one release, and he appeared to be in pain as he shook his hand coming off the field. The injury was iced, and X-rays later showed no break, according to Rueben Frank of CSN Philly.

Crisis averted.

But it seems as if Vick is always one play away from missing time. In nine NFL seasons, Vick has completed 16 games just one time. While not fragile, per se, Vick does open himself up to a lot more punishment than most NFL quarterbacks.

If the Eagles are to avenge their disappointing 2011 campaign, they need Vick healthy for most of 2012. The question is, can he provide 16 injury-free starts?

The Vikings have been very cautious with Peterson, who had his knee surgically reconstructed late last season after a devastating injury. He has yet to practice and remains on the preseason PUP list.

According to Tom Pelissero of ESPN1500 in the Twin Cities, Peterson has numbness in the area of his knee where the nerves were cut. While not unusual, it does help illustrate the kind of injury Peterson is attempting to come back from.

The Vikings aren't going to rush back Peterson, nor should they. If he's ready for contact by the third or fourth preseason game, great. If not, keep him shelved.

Either way, running backs coming back from this injury usually need at least another full year before feeling 100 percent healthy. Peterson is a physical marvel, but question marks will remain.

Manning made his Broncos debut Thursday night, and it came and went with little drama or worry. He led the Broncos into the red zone on one series, but threw behind Brandon Stokley inside the 10-yard line and was intercepted.

Still, it's worth noting that Manning is on the record saying he's still far from 100 percent health-wise. According to Peter King of Sports Illustrated, Manning's nerves are still in recovery mode.

It's not his neck, which has undergone four procedures in the past two years, including the major surgery 11 months ago that caused him to miss the 2011 season. It's simply the regeneration of the nerve that affects his arm strength, particularly the area around the shoulder.

The man has undergone at least four neck surgeries in the last 20 months, so question marks should come as part of the package. We just don't have a grasp yet on how the repaired neck will hold up over the course of a long NFL season.

Hakeem Nicks, WR, New York Giants

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Nicks broke his foot during an offseason team drill in late May, but all indications were that he'd be healed from surgery in time for the start of the regular season. So far, so good.

According to Ralph Vacchiano of the New York Daily News, Nicks will begin running routes at the Giants practice Tuesday, and he's still on track to be ready for Week 1.

The recovery is still a concern moving forward, however.

Foot problems have a tendency to linger, especially with receivers. Nicks better be sure he's ready to go next week, because setbacks happen all the time with these injuries. Keep an eye on this one as the regular season inches closer.